Small-cap stocks can make for rather exciting investment opportunities. After all, even a modest investment in a small-cap stock has the potential to turn into a large sum if the company performs well. But small-cap stocks tend to be more volatile than their large-cap counterparts.

Having said that, there are some small-cap stocks that look like excellent long-term growth opportunities, but without a disproportional amount of risk. Here's why fintech company Green Dot (NYSE:GDOT), outlet mall REIT Tanger Factory Outlet Centers (NYSE:SKT), and online bank Axos Financial (NYSE:AX) could be worth a look right now.

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An under-the-radar fintech with lots of potential

Green Dot isn't exactly a household name, but that could certainly change in the future. The company is best known as an issuer of prepaid debit cards, but there's a lot more to it than its core product. In addition to its prepaid debit cards, which are readily available at retailers across the U.S., Green Dot offers other banking products, such as its GoBank bank accounts. However, it's the company's "banking as a service," or BaaS, platform that I'm most excited about.

Essentially, how Green Dot's BaaS business works is that it allows other companies, which have no desire to become banks themselves, to use a piece of its technology and infrastructure to offer banking products to their customers. Think of things like person-to-person payment apps, or company-branded payment cards.

To name some examples, the Apple Pay Cash person-to-person payment platform is powered by Green Dot, as is the Walmart MoneyCard prepaid Mastercard product. Green Dot is also the technology behind Uber's Instant Pay, which allows drivers to get paid for their services immediately. Green Dot has added several new partners over the past couple of years, and I wouldn't be surprised if this is just the beginning.

Take advantage of retail weakness

Many investors are hesitant to put their money into the retail industry, and I can't say that I blame them. However, one retail investment that is still worth considering is real estate investment trust Tanger Factory Outlet Centers, which owns and operates outlet malls under its own brand name.

While lots of retailers are indeed struggling, there are some that are actually doing quite well. Specifically, most retailers with an experiential component or a discount-oriented approach are holding up nicely in the face of growing e-commerce competition. Outlet shopping checks both of those boxes. Plus, outlet retail is somewhat recession-resistant. As CEO Steven Tanger puts it, "In good times people love a bargain, and in tough times people need a bargain."

Tanger pays a 6% dividend yield, which is well covered by its funds from operations -- the REIT version of earnings -- so it isn't likely that the company's 25-year streak of dividend raises is in jeopardy. This REIT could be an excellent combination of income and growth, and could produce excellent long-term returns in your portfolio.

New name, same great opportunity

It's been a busy year for Axos Financial. In addition to changing its name from Bank of Internet USA, Axos has made a few acquisitions, such as Nationwide's deposit base, and has invested heavily in a new initiative it calls the Universal Digital Bank (UDB).

My Motley Fool colleague Billy Duberstein does a great job of explaining the UDB idea in this recent article, but essentially the UDB platform combines all of Axos' products and services into one unit, allowing for more cross-selling potential and customized solutions for customers.

The main reason I love Axos is its low-cost business model, which gives it a big advantage over its brick-and-mortar peers. For example, Axos generated a 15% return on equity in the most recent quarter -- far in excess of the 10% industry benchmark.

Plus, with less than $10 billion in assets, Axos is a rather small banking institution, but is growing fast. On a year-over-year basis, net income has increased by nearly 14%, and the bank's loan portfolio has increased by more than 15%. And I think the new UDB initiative could cause its growth to accelerate.